1. Field of the Invention
The present invention relates to ATA host controllers on a PCI card. More specifically, a computer subsystem constructed by daisy chaining a plurality of dominant chips comprising ATA host controllers on a single PCI card is disclosed.
2. Description of the Prior Art
A peripheral component interconnect (PCI) card makes quick and easy expandability commonplace in modern computer systems. Designed by Intel and released in 1993, the PCI interface has long been incorporated into virtually all personal computers and provides a near universal platform for a plethora of variously functioning PCI cards.
Conventionally, a PCI card is designed to perform a specific function and comprises a dominant chip on the card that performs that function. For example, a PCI graphics card comprises a dominating graphics chip that does most of the work. The card itself basically provides an interface between the graphics chip and the rest of the computer system. Another example is a PCI card designed to operate a redundant array of inexpensive disks (RAID) system comprising two hard disk drives. This card would comprise a dominant chip comprising a host controller that operates the RAID system for the two disks.
Both the graphics chip and the chip that operates the RAID system have built in parameters limiting the workload of each chip. The graphics chip is only capable of producing so many triangles per second. The RAID chip is only capable of servicing two hard drives. If a system requires a function in excess of the limits provided by the dominant chip, such as servicing four hard drives, the common solution is to simultaneously utilize a second PCI card comprising the same dominant chip. Thus, two PCI graphics cards can increase the number of triangles processed per second and two PCI RAID cards can double the number of hard drives available for a given system.
The problem with this solution is that the number of PCI slots in a computer system is limited and a free PCI slot may not be available. Redesigning backplanes or motherboards comprising additional PCI slots is expensive. Furthermore, a design including additional PCI slots is considered an uncompetitive redundancy because each PCI slot is already capable of providing eight different functions. Because the conventional PCI card often utilizes only two or three of the eight possible functions, much of the capability of the PCI slot is wasted, reducing the motivation to provide additional PCI slots. Redesigning the dominant chip to higher functional limits, such as altering the RAID chip to control 4 disk drives, is another possible solution, but is difficult and usually economically unfeasible.